These are not apps. And none of these are meant to run on a server like Wordpress. If you run less or babel compiler on production servers to serve CSS or JS well , you're not a serious developer.
Cloud9 I guess would be a good example of a killer app ,but that's no CMS.
The reason why there is no serious CMS with node is that nodejs development is extremely hard, because async programming is hard. No matter how much layers one puts on top of it (promises,generators...) you can't abstract async programming in nodejs.
Look at Go, Go routines can be totally abstracted. IF I write that code:
result := Object.DoNonBlocking()
As a client of Object I don't have to know whether it is run concurrently, or not , or blocking or not. In node I have to know whether I returns a promise or a value , IE hump into the event loop or not.
PHP has its share of problems though,just like Go, but their concurrency model(or lack of) make things way more easy.
I can't imagine writing something such as Magento or Drupal in nodejs (with the exact same features). It would be just insane. A great challenge though.